1. Field of the Invention
The present invention relates to an electroacoustic transducer, and, more particularly, to an electroacoustic transducer, which has a magnet support portion in a support member which supports a diaphragm comprising an elastic plate (also called a resonance plate) and an added mass attached to the center of said elastic plate, and hence, the magnet support portion supports the magnet between a base and the magnet support portion, thereby an unexpected detachment of the magnet from the base is prevented.
2. Description of the Related Art
A structure of an electroacoustic transducer as an example of the prior art is illustrated in FIGS. 11 and 12. There is a case 401, and formed at the center of the left-hand end portion in FIG. 12 is a sound port 403. The case 401 is provided with a support ring 405 at the inner wall of the right-hand portion in FIG. 12. There is an opening 407 formed in the right-hand end portion in FIG. 12. A base member 409 is secured to the opening 407. The base member 409 comprises a core 411 attached to the center thereof, and also a board 413 attached thereto.
A coil 415 is wound around the core 411. The respective terminals of the coil 415 are securely connected, by means of solder, for example, to lead terminals 417 and 419 attached to the board 413. A magnet 423 is placed around the coil 415 with an existence of a ring-like clearance 421 formed in between. The aforementioned support ring 405 is provided at the outer periphery of the magnet 423, having a step portion 425 at which a diaphragm 426 is supported. The diaphragm 426 comprises an elastic plate 427 and a magnetic piece 429 which are attached as an added mass to the center portion of the elastic plate 427.
In the thus constituted electroacoustic transducer, the elastic plate 427 integrally provided with the magnetic piece 429, is set to have a given polarity by means of the magnet 423, and hence, is attracted to the magnet 423. When a current flows across the coil 415 via the lead terminals 417 and 419 under this situation, the core 411 is magnetized, generating a magnetic field at the distal end thereof. When the magnetic pole of the core 411 induced by the coil 415 is different from the magnetic pole induced by the magnet 423 attached to the elastic plate 427, the elastic plate 427 is attracted to the core 411. When the magnetic pole of the core 411 induced by the coil 415 is the same as the magnetic pole induced by the magnet 423 attached to the elastic plate 427, the elastic plate 427 repels the core 411. Consequently, by allowing the current to intermittently flow in either direction, the elastic plate 427 repeats the above-discussed operation. In other words, the elastic plate 427 vibrates at a given frequency, thus generating a sound.
There is another type of electroacoustic transducer of which structure is shown in FIGS. 13 and 14. There is an upper case 501, and the upper case 501 has a base member 503 attached to the bottom thereof. A base 505 and a core 507 are integrally secured inside the upper case 501 (on the base member 503). The integrated material of the base 505 with the core 507 is called "pole piece". A coil 509 is wound around the core 507, and a support ring 511 is placed around the coil 509. A magnet 513 is provided on the inner wall of the support ring 511. A ring-like clearance 515 is formed between the magnet 513 and the coil 509.
Formed at the left-hand end portion of the support ring 511 in FIG. 14 is a step portion 517 at which a diaphragm 518 is provided. The diaphragm 518 comprises an elastic plate 519 and a magnetic piece 521 attached as an added mass to the center portion of the elastic plate 519. As seen in FIG. 13, lead terminals 523 and 525 have previously been implanted in an integral manner to the base member 503 by inserting. In the thus discussed structure, both coil terminals 509a and 509b of the coil 509 are respectively led out on the lead terminals 523 and 525, and are securely soldered to those lead terminals 523 and 525.
Since the action of the present type of electroacoustic transducer is the same as that of the electroacoustic transducer as discussed with reference to FIGS. 11 and 12, the description of such an action will not be repeated.
As regards the electroacoustic transducer according to the above discussed prior arts, there exists some problems as follows.
In the case of the electroacoustic transducer as illustrated in FIGS. 11 and 12, the magnet 423 is attracted to and fixed on the base member 409 by means of magnetic force, further the magnet 423 is adhered to and fixed on the base member 409 by means of adhesive. Such a type of electroacoustic transducer is mounted on a various type of electronic instruments, such as a portable telephone, etc., and when the electroacoustic transducer is mounted on the portable telephone, for example, the resistance against the drop shock at about 10,000 G-force is often required. However, when the above amount of shock is given to the conventional structural type of electroacoustic transducers, there is a possibility that the magnet 423 may peel off the base member 409. When the magnet 423 peels off the base member 409, the detached magnet 423 may be attracted to the elastic plate 427, otherwise may collide against the elastic plate 427, which results in deformation of the elastic plate 427, and hence, the desired acoustic performance is spoiled.
The magnet 423 peels off the base member 409 due to the following reasons. Namely, the magnet 423 is made of any metal of which specific gravity is greater, for example, samarium-cobalt, ferrite, iron-cobalt chromium, etc., in order to obtain a desired magnetic force. However, such metals are very hard in solidity, therefore the cutting is difficult, and instead, the grinding is usually performed at the finishing. As above discussed, the magnet 423 is made of metal of which finished surface is ground almost like a "mirror surface", the adherent strength by adhesive may not be sufficiently obtained, and hence, the desired adherent strength may not be obtained. Consequently, when any shock is given, the magnet 423 may peel off the base member 409.
There may be an adhesive available of which adherent strength is greater, but such an adhesive is usually very expensive, which leads to increase in costs.
There is a likewise problem in regard to the magnet 513 as illustrated in FIGS. 13 and 14.
The present disclosure relates to subject matter contained in Japanese Patent Publication Nos. 07-117837 and 07-117838, which are expressly incorporated herein by reference in their entireties.